Vertical Communications DSU and DSU II - Manual (Page 45)

2.15 Operating Your Telephone
With A DSS/BLF Console
The IB64X, IB48X, and IB24X DSS/BLF consoles have additional
buttons and status lights that extend the memory button capability of an
adjacent companion telephone. The buttons can be programmed for
automatic dialing (speed dial) or direct station selection (DSS) with
busy lamp field (BLF) using the instructions provided previously in this
guide.
When the installer assigns a DSS/BLF console to a station port, the
system recognizes it as such and automatically designates the console
buttons as DSS buttons so that you can store numbers at the buttons as
you need them.
The DSS/BLF console will not operate in a bridged mode.
ib64x
IB64X DSS/BLF Console
GCA70–245 Programming The Attendant Features
LCD Speakerphone Reference Manual 2–25